As a liquid crystal display device employing a liquid crystal material, a TN mode liquid crystal display device is in practical use. In such a mode, light switching is carried out by utilizing the optical rotation property of a liquid crystal, and a liquid crystal display device in this mode requires use of a polarizing plate. However, use of a polarizing plate lowers light utilization efficiency.
As a liquid crystal display device which achieves high light utilization efficiency without using a polarizing plate, a liquid crystal display device in which switching is conducted between a transmission state (also called a transparent state) and a scattering state of a liquid crystal may be mentioned, and a liquid crystal display device employing a polymer dispersed liquid crystal (PDLC) or a polymer network liquid crystal (PNLC) is commonly known.
A liquid crystal display device employing such a liquid crystal is a liquid crystal display device having a liquid crystal layer, that is, a cured product composite (for example, a polymer network) of a liquid crystal and a polymerizable compound, formed by disposing, between a pair of substrates provided with electrodes, a liquid crystal composition containing the polymerizable compound which undergoes polymerization by ultraviolet rays and curing the liquid crystal composition by irradiation with ultraviolet rays. In such a liquid crystal display device, the transmission state and the scattering state of the liquid crystal are controlled by application of a voltage.
A conventional liquid crystal display device employing PDLC or PNLC is a liquid crystal display device (a normal device) which is in a cloudy (scattering) state when no voltage is applied, since liquid crystal molecules are randomly aligned, and is in a transmission state when a voltage is applied, since liquid crystal molecules are aligned in an electric field direction, whereby light is transmitted. However, in a normal device, it is necessary to always apply a voltage in order to obtain a transmission state, and accordingly when it is used for an application which is mainly used in a transparent state, for example, when used for window glass, the electrical power consumption tends to be large.
On the other hand, a liquid crystal display device employing PDLC (a reverse device), which is in a transmission state when no voltage is applied and is in a scattering state when a voltage is applied, has been reported (e.g. Patent Documents 1 and 2).